1. Field of the Invention
The present invention relates to rotary printing presses and more particularly to apparatus for holding a flexible printing plate in position on a rotary printing plate cylinder. The printing plate which comprises a flexible blanket holding the image that is to be printed is aligned and clamped at its leading end by a plate clamp mechanism and is engaged by a tail clamp mechanism at the trailing end. The tail clamp mechanism grips the tail end of the plate and applies tension causing the plate to lay flat against the cylinder.
2. Description of the Prior Art
In present day rotary printing presses flexible printing plates hold the image that is to be printed and the plates are held in position on rotary printing cylinders using various mechanisms. Generally, the leading edge of the plate is located in registry and securely held by a plate clamp and the trailing edge of the plate is held by a mechanism that applies tension on the plate to hold it against the surface of the rotary printing cylinder. These mechanisms generally consist of bars that extend axially across the cylinder adjacent the outer surface and contact the leading and trailing edges of the plate. This arrangement requires a large circumferential gap in the cylinder wall, limiting the effective printing surface area of the cylinder. In addition, the bar clamping mechanisms do not open widely enough, requiring the operator to insert the plate into an inconveniently narrow opening. The following listed U.S. patents are examples of prior art devices of the character described:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 4,223,604 Brehm et al. 4,367,679 Ishi et al. 5,182,994 Sugiyama et al. 5,272,978 Wehle et al. ______________________________________
U.S. Pat. No. 4,831,931 to Jeschke et al. discloses another type of plate clamping apparatus wherein tensioning devices are located on both the leading and trailing end of the blanket. Although the Jeschke et al. patent as well as the Sugiyama et al. U.S. Pat. No. 5,182,994 listed above disclose examples of clamp actuating mechanisms utilizing either internal or external fluid or electrically driven motor means, most prior art sheet clamping and tensioning systems must be operated by hand using a tool or other device to tighten or loosen the clamping mechanism. U.S. Pat. No. 5,272,978 to Wehle et al. and U.S. Pat. No. 4,367,679 to Ishii et al. both utilize locking screws or rotary knobs to actuate the tensioning devices. U.S. Pat. No. 4,223,604 to Brehm et al. discloses still another type of operator typical of the hand operated key type. This type of actuation requires the operator to let go of the sometimes large and unwieldy plate to operate the clamping mechanism.